1. Field of the Invention
The present invention relates to an exposure apparatus used in a semiconductor manufacturing process and, more particularly, to a projection exposure apparatus which projects and transfers an exposure pattern formed on an original plate onto a substrate.
2. Description of the Related Art
Conventionally, an exposure apparatus used in a semiconductor manufacturing process comprises a stage device having a coarse moving stage which rapidly accelerates/decelerates with a high acceleration/deceleration, and a fine moving stage which accurately aligns a substrate. To save the alignment waiting time and to improve the throughput, such an exposure apparatus parallelly executes alignment measurement and exposure by swapping the positions of two stages between an alignment measurement area and an exposure area. This processing is called a swap.
JP2005-353969A discloses a technique of interposing intermediary interferometers between a plurality of interferometers which measure the positions of coarse moving stages. The intermediary interferometer passes the measurement result obtained by one interferometer to the other interferometer before and after a swap, thereby improving the alignment accuracy of a stage device in an exposure station.
Unfortunately, JP2005-353969A does not describe how to measure the distance between an optical system support and a stage surface plate. Even when the stage surface plate deforms or its position changes before and after a swap operation, it is impossible to detect any misalignments of stages due to such factors. As a consequence, the alignment accuracy of the stage device deteriorates after the swap operation, so alignment or the like must be repeatedly performed. This results in prolongation of the processing time per wafer.